1. Field of the Invention
The present invention relates to an X-ray CT apparatus that reuses regenerative energy and a method of controlling the same.
2. Description of the Related Art
In the field of an X-ray computer tomography apparatus (an X-ray CT apparatus) that performs tomography of a subject by using X-rays, efforts have been made on a daily basis in various aspects such as the facilitation of multifunctionality, sophisticated performance, and the shortening of imaging time. However, the amount of heat that is released tends to increase as the performance and functionality of these apparatuses improves.
As such technological innovation advances, the issue of how to externally release the heat that is generated as a byproduct inside the apparatus has been studied in conjunction.
A representative of the heat generated inside the X-ray CT apparatus is attributable to the regenerative resistance. Regenerative resistance is a resistance element that is provided to convert into heat energy electromotive force energy generated during the deceleration of the rotation of a motor for driving a rotating body that performs tomography of a subject while rotating (e.g., direct drive motor or the like). Therefore, when the motor frequently accelerates/decelerates, such as when consecutively imaging multiple subjects or when a service engineer performs maintenance or the like, the regenerative resistance may reach a considerable temperature. As a constitution for addressing such a situation, the technology of simply increasing the quantity of regenerative resistance, and furthermore, for example, the following technologies have heretofore been known.
Some X-ray CT apparatuses are installed so that heat tends to be released outside the apparatus by providing regenerative resistance on the upper portion of a mounting base, and often adopts a constitution that brings the regenerative resistance is contact with a metal portion within the mounting base to enable the heat to escape from the metal portion.
Meanwhile, for an X-ray CT apparatus in which it is difficult to ensure a sufficient space for installing the regenerative resistance on the upper portion of a mounting base, the lateral portion of the apparatus is often provided with the regenerative resistance.
Among the X-ray CT apparatuses as described above, those having an additional constitution such as a fan for externally guiding the heat generated by the regenerative resistance has also heretofore been known. For example, Japanese Unexamined Patent Application No. H9-276262 discloses an X-ray CT apparatus that is provided with a suction opening on the upper portion of the imaging opening and with a cooling fan on the upper portion of the apparatus respectively and releases the heat by generating airflow inside the apparatus.
In addition, an X-ray CT apparatus has been proposed that is configured to release the heat inside the apparatus by rotating a plurality of blade members along with a rotating part of a mounting base to convey air to a supporting member (X-ray computer tomography apparatus, e.g., Japanese Unexamined Patent Application No. H9-56710).
Similar to the constitution described in Japanese Unexamined Patent Application No. H9-276262, this also attempts to release the heat by keeping favorable ventilation inside the apparatus.
Moreover, an X-ray CT scan system has been disclosed comprising a regenerative resistance apparatus provided inside the mounting base (X-ray CT apparatus) and a blower fan for transferring the heat generated by this regenerative resistance apparatus to a top plate of a carrying apparatus on which to place a subject (e.g., Japanese Unexamined Patent Application Publication No. 2002-336236). This X-ray CT scan system makes it possible to achieve a heating action for a subject by warming the top plate. It also adopts the method of cooling the regenerative resistance by using airflow.
In addition, technology has also been proposed of accumulating the regenerative energy in a condenser without change to reuse the same (e.g., Japanese Unexamined Patent Application Publication No. 2006-289066).
Herein, by way of example, a conventional X-ray CT apparatus with a constitution in which heat is released by a regenerative resistance will be described below with reference to FIG. 1 and FIG. 2.
FIG. 1 is a front perspective diagram showing an outline of the constitution of a conventional X-ray CT apparatus. In addition, FIG. 2 is a block diagram showing the constitution of a conventional X-ray CT apparatus. As shown in FIG. 1, an X-ray CT apparatus 1 is an apparatus for irradiating X-rays while scanning a subject and for detecting the X-rays that have permeated the subject. This X-ray CT apparatus 1 constitutes an X-ray tomographic imaging system along with a bed for carrying a subject placed on a top plate to the imaging position (imaging opening described above), a computer for analyzing the detected data of the X-ray CT apparatus 1 to reconstruct and display the X-ray tomographic image (neither are shown) or the like and uses the same.
An opening provided near the center of a package 2 of the X-ray CT apparatus 1 forms an imaging opening 3 into which the subject placed on the top plate described above is to be inserted. The package 2 houses a wide variety of instruments for irradiating X-rays at a subject from various directions and detecting the X-rays that have passed through the subject, including a motor 4 such as a direct drive motor, a rotating body 5, an inverter part 6, and the like. In addition, a regenerative resistance 7 is connected to the inverter part 6.
The rotating body 5 is a frame body that is arranged so as to surround the imaging opening 3 and is rotated by the motor 4. On the rotating body 5 (supporting unit), an X-ray tube 8 (X-ray-generating unit) for outputting X-rays and a detector 9 (detecting unit) for detecting the X-rays outputted from this X-ray tube 8 are supported in an opposing arrangement. In addition, an AC/DC converter 10 for supplying a power source to the X-ray tube 8 and the detector 9, a signal-processing apparatus 11 for processing the results of detection by the detector 9, and the like, are attached to the rotating body 5.
The inverter part 6 comprises IGBTs (Insulated Gate Bipolar Transistors) 12 or the like. The inverter part 6 adjusts the voltage and frequency of the power source to be supplied to the motor 4 based on signals sent from the control part (control unit) and controls the drive, stopping, rotational speed, and the like of the motor 4. Incidentally, the motor 4 and the inverter part 6 constitute a drive unit in the present invention.
The regenerative resistance 7 is a member for converting the electrical energy (regenerative energy) that is generated during the deceleration of the motor 4 and flows backward into the inverter part 6 to be converted into heat energy for consumption of the same.
Incidentally, a regenerative resistance is also provided within the inverter part 6, while the regenerative resistance 7 is used in consuming regenerative energy that cannot be processed by this embedded regenerative resistance. Herein, the regenerative resistance 7 is installed, for example, on the upper portion of the side surface of the package 2 of the X-ray CT apparatus 1, as is conventionally done, and is structured so as to be thermally connected to a heat-releasing member or the like for releasing heat externally.
Each member installed in such a manner is configured as shown in FIG. 2. As shown in FIG. 2, the AC/DC converter 10 is connected to the motor 4 via the inverter part 6 consisting of switching elements such as IGBTs. The regenerative resistance 7 is interposed into the transmission path between the AC/DC converter 10 and the IGBTs and, during the deceleration of the motor 4, conveys the generated regenerative energy to the regenerative resistance 7 connected to the heat-releasing member for conversion of the same into heat.
In an X-ray CT apparatus with such a constitution, firstly, the imaging processing by an X-ray tomographic imaging system including the X-ray CT apparatus 1 is executed, in the process as follows. In FIG. 2, the switch SW1 is initially connected to the AC/DC converter 10.
The X-ray CT apparatus 1 supplies power from the inverter part 6 to the motor 4 to rotate the rotating body 5, irradiates X-rays from the X-ray tube 8, and detects the X-rays that have permeated the subject who is moved into the imaging opening 3 by the detector 9.
Then, the X-ray tube 8 and the detector 9 operate by receiving power from the AC/DC converter 10. The permeated X-rays that have been detected by the detector 9 are processed by the signal-processing apparatus 11 and converted into image data, and are then sent to the computer described above. Then, this computer reconstructs the image data into an image and displays a tomographic image of the subject.
After the imaging processing described above has been repeatedly executed, the energy based on the return electromotive force during the deceleration of the motor 4 (detected by the control part 100 itself), that is regenerative energy, is generated in a large amount. This regenerative energy is sent to the regenerative resistance 7 by the control part 100 turning on the switch SW1 into the side of the regenerative resistance 7, and the heat is released by a heat-releasing member thermally connected to the regenerative resistance 7.
However, the development of X-ray CT is currently moving in the direction of reducing the burden on a subject by shortening the imaging time. Thus, in order to shorten the imaging time, it is necessary to shorten the scanning time. In other words, it is necessary to rotate the rotating body at a higher speed, that is, to control the motor at high-speed rotation. In this regard, however, because the motor must be rapidly accelerated/decelerated in order to achieve this objective, a larger amount of regenerative energy is generated than in the past, so technology for effectively releasing heat or efficiently reusing the generated large amount of regenerative energy is required.
In other words, a so-called air-cooled heat releasing function described in Patent Documents 1 through 3 requires a large-capacity regenerative resistance for the release of heat energy increased by the accelerated rotation of the rotating body, thereby making it difficult to achieve a simplification of the constitution and a reduction in the manufacturing cost.
In addition, for the technology described in Patent Document 4, it is difficult to make the X-ray CT apparatus more compact, because regenerative energy is accumulated without change and the capacity of the accumulating portion thus becomes larger.